Removing entrained gaseous fluids from solids



noun.

H. z MARTIN 2,458,866

REMOVING ENTRAINED GASEOUS FLUIDS FROM SOLIDS 2 Sheets-Sheetl Jan. 11, 1949.

Filed Nov. 21, 1944 Tae FIQ-l Jlomer "Z. artz'n, Unvenboz Gbbornaq Jan. 11 1949. H, z -[1N 2,458,866

REMOVING ENTRAINED GASEOUS FLUIDS FROM SOLIDS Filed Nov. 21; 1944 2 Sheets-Sheet 2 -15 v Aim A AAMAAAAAA A455 AAAAAAA-A-4 b A-AAAAAA-442 Patented Jan. ll i949.

REMOVING ENTRAINED GASEOUS FLUIDS FROM SOLIDS Homer Z. 'Martin, Roselle, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application November 21, 1944, Serial Nil- 584,515

8 Claims. (Cl. 23-288) This invention relates to stripping or purging volatile entrained material from solid particles. Invarious catalytic processes using powdered catalyst or contact material or catalyst or contact "material in divided form, volatile material is entrained with the particles removed from the reaction vessel or zone. For example, in the, cata-' lytic cracking of hydrocarbons, coke or hydrogencontaining carbonaceous material'is deposited on the catalyst or contact particles and the particles are usually removed from the reaction zone and passed to a regeneration zone where they are regenerated' In removing catalyst or contact particles from the reaction zone, volatile hydrocarbons are entrained with the particles, and if the volatile material is not substantially all removed from the particles, it is lost from the system by being burned-in the regeneration zone. Also, in such cases,: an additional load is placed on the regeneration zone as more combustible material must be burned.

In, the newer type unit for catalytic cracking, the solid particles are maintained as a dense dry fluidized liquid-simulating mixture in the lower portion of the reaction zone with a dilute phase thereabove. In these newer units greater quantitles of catalyst are circulated to and from the reaction zone since all the heat for preheating, vaporizing and cracking the oil is transferred by direct contact of hot regenerated catalyst with the relatively cold oil feed. Poor stripping is therefore reflected in greater product loss and greater carbon or coke formation than in the older type units not using liquid feed. In the newtype'units the spent or fouled catalyst or contact particles are removed as a dense fluidized dry liquid-simulating mixture and the stripping step usually used is not as efllclent as is desired. In the older type units the stripping was done in the dilute phase. The essential difi'erence be tween the dilute'and the dense bed stripping sections is that in the dilute phase stripping the gas phase predominates in the stripping section.

usually provided in the catalyst entrance point so that the. catalyst particles cannot completely fill the stripping section. The solid particles then fall through a. stream of slowly rising gases and in this way are effectively stripped of whatever hydrocarbonmaterials they bring into the stripping section.

According to this invention, dense phase fluidized spent or fouled catalyst is removed from the lower part of a reaction zone and passed through a stripping section as .a dilute phase mixture or as a mixture in which there is only a small amount of particles suspended in the stripping gas. With my invention better stripping is obtained and less steam or other stripping gas is required than with the dense phase stripping operation.

The material stripped out is returned to the dilute phase in the reaction zone and thus by passes the dense bed permitting more effective use of the reaction zone or use of a smaller reaction zone. Or the material stripped out may be passed to other separating equipment to reduce the load on the separating equipment associated with the reaction zone.

In the drawings:

Fig. 1 represents one form of treating unit embodying my invention;

Fig. 2 represents a horizontal transverse enlarged cross-section taken substantially on line 2--2 of Fig. 1 with parts broken away to facilitate the disclosure; Fig. 3 represents a partial developed sectional view taken substantially on line 3-3 of Fig. 2; and

Fig. 4 represents a vertical longitudinal section taken substantially on line 4-4 of Fig. 2.

Referring now to the drawing, the reference character l0 designates a reaction or contact zone provided with a feed inlet pipe 12 which extends into the reaction zone and terminates in a conical member l4 having a horizontally arranged perforated distribution member H5 at its upper end. The conical member [4 is arranged in the lower portion of the reaction zone or vessel Ill.

The feed may be vaporizeipreheated liquid or a mixture of vapors and liquid. When using preheated liquid or a'mixture of vapors and liquid,

hot regenerated catalyst is used in sufllcient amount to vaporize all the liquid and raise the liquid or vapors to reaction temperature. When 3 using vapors as the feed, the vapors and not regenerated catalyst are mixed and introduced into the reaction zone or vessel I 0.

The feed is introduced into line I! through line l8 and hot regenerated catalyst or contact particles are introduced from line 22. The mixture is passed through line I! and distribution member i6 is through the reaction zone ID, the distrlbution member I 6 acting to evenly distribute the solid particles across the areapt the reaction zone. If desired, the feed and catalytic or contact materal may be separately introduced into the reaction zone.

When hydrocarbons are to be catalytically cracked, the catalyst is any suitable cracking catalyst, such as acid-treated bentonite clay, silica alumina gel, or-silica magnesia gels, etc., having when other hydrocarbon treating operations are When used, such as catalytic reforming, etc. catalytic treatment of other materials is used. suitable catalysts are selected.

The velocity of th vapors or'g'ases passing up- 4 particles must be regenerated before being reused in another cracking operation or treating operation. In the type of unit shown in Fig. 1 of the drawing. the spent or fouled catalyst is withdrawn from the bottom portion of the reaction zone in a dense phase or dense dry liquid-simulating condition. 7

My invention comprises an improved stripping zone or section which will now be only generally described to complete the process and then my improved stripping section or vessel will be more particularly described. The dense phase spent catalyst is passed through an annular stripping zone or section 44 arranged below the level 01 the distribution plate I 6 where the catalyst particles are contacted with a stripping gas, such as steam, introduced into the bottom portion of the stripping zone or section 44 through line 46. The stripping gas flows upwardly countercurrent to the downflowing catalyst particles.

The stripped catalyst or contact particles collect in the conical bottom ll of the cylindrical reaction vessel I0 and' are preferably maintained in a fluidized condition by the introduction of fluidizing or aerating gas at 52. Stripped catalyst or contact particlw flow into the spent catalyst wardly through the reaction zone or vessel It is 7 selected to form a dense fluidized dry liquid-simulating mixture 24 having a level 26 with a dilute phase or dilute suspension 28 above the dense phase. The dense mixture 24 is maintained in a highly turbulent and agitated condition to in-' sure intimate contact between the gaseous. fluid and the contact particles. Using acid-treated bentonite clay in powdered form and with a velocity between about it lit/second and 1V: it./second, the density of the fluidized mixture is between about 12 lbs./cu. ft. and 30 lbs./cu. f t. The temperatures during the cracking operation may vary between about 700 F. and 1100 F. Pressures are usually about atmospheric but higher pressures may be used if desired.

Gas, such as, steam. may bcintroduced into line I! through line 32 for admixture with the feed and the hot regenerated catalyst. The vapors or gaseous fluid passing upwardly through the reaction zone remains in the reaction zone for a sumcientp flod 01' time to eflect the desired extent of reaction or conversion. The gaseous reaction productspass upwardly into the upper part of the reaction zone or vessel l0 and some. catalyst or contact particles settle out and some are entrained in the reaction products into the dilute phase 28.

The gaseous reaction products are passed through a separating means 38 arranged in the upper part of the reaction zone or vessel ll to. remove the entrained catalyst particles from the gaseous reaction products. Separated catalyst is returned to the dense bed 24 by dip pipe 38 which dips below the level 28 of the dense bed mixture 24 in the reaction zone II. The gaseous reaction products pass overhead through line 42 to a suitable equipment (not shown) to recover desired products. In catalytic cracking the reaction products are passed to a iractionating equipment wherein the desired products are separated and entrained catalystis recovered by the condensate oil in the bottom portion of the tractionator.

The catalyst or contact particles during the catalytic reaction where organic material is being' reacted, such as the catalytic cracking of hydrocarbons, become fouled or spent by the deposition oi coke or carbonaceous material and the catalyst standpipe it having a control valve 56 for controlling the rate of flow of catalyst from the spent catalyst standpipe 54. A level controller, generally indicated at 58, is provided to maintain the level of stripped catalyst at about the level shown at 52 in the drawing by varying the opening of cgntro'l valve 56 on the spent catalyststandpipe I The stripped spent catalyst is mixed with a regenerating gas, such as oxygen, oxygen-containing gases, air, etc., introduced through line 62 to form a less dense mixture and the less dense mixture is passedthrough line it into the conical bottom portion 66 of the cylindrical regeneration zone or vessel 60 below perforated distribution plate member 12. The velocity'of the regenerating gas is 1 selected to iorm a dry fluidized liquid-simulating mixture or bed ll of catalyst particles having a level indicated at 16 with a dilute phase 18 thereabove. The catalyst or contact particles in the fluidized mixture or bed are maintained in an agitated and turbulent condition to insure intimate contact between the regenerating gas and the particles to be regenerated. With this form of mixture, the temperature during regeneration is maintained substantially constant throughout the regeneration step. The upper portion of the regeneration zone or vessel It forms a settling zone and some catalyst settles out of the regeneration gases and some is entrained with the regeneration gases leaving the dense bed or mixture 14.

Hot regeneration gases pass into the separating means 82 for separating some entrained catalyst particles from the regeneration gases. The separating means I2 is arranged in the upper portion of the regeneration vessel 68. Separated catalyst is returned to the dense bed or mixture 14 by dip pipe I} which extends below the level 16 in the regeneration zone 88; Hot regeneration gases pass overhead through line". Additional separating means may be used, such as cyclone separators, scrubbers, electrical precipltators, etc.

The temperature during regeneration is about 1000 F. to 1150 F. and before passing the regenthrough a heat exchange equipment such as a waste heat boiler.

Hot regenerated catalyst at a temperature of about 1000 F. to1150 F. is withdrawn in a dense fluidized condition from the lower portion of the dense bed 14 through withdrawal pipe 88 which extends above the distribution plate member I2. Pipe 88 forms the upper part .0! regenerated catalyst standpipe 82 which receives the hot regenerated catalyst from the pipe 88 and which feeds the regenerated catalyst to lines 22' and I2 leading to the reaction zone or vessel I0. Fluidizing lines 84 are provided for the regenerated catalyst standpipe 92 for maintaining the catalyst particles in a dense fluidized liquid-like condition in the standpipe to produce a. suflicient hydrostatic pressure at the bottom of the standpipe to return the regenerated catalyst particles to the reaction zone or vessel I0.

Standpipe 92 is provided with a control valve 96 at its lower portion for controlling the rate of I now be described. The entrance to the stripping section 44 is providing with ports or openings I02 controlled by valves I04. The valves are provided with actuating means I06 which extend outside reaction vessel I for varying the size of the ports or openings I02. While I have shown four ports and four valves, it is to be understood that the number of openings in the valve maybe varied.

The valves may be manually or automatically controlled and may be individually operated or operated as a unit. The valves may be butterfly or pivoted valves, plug valves, slide valves, or other suitable types of valves.

Curved arcuate baffles I08 are provided between ports I02. As shown in Fig. 3, these bafiies are preferably curved or arched upwardly from the ports to prevent catalyst build up at the ports I02 or at the entrance to the stripping zone 44. The bafiles I08 may take other shapes as inverted V shapes in cross section, the shape being selected to prevent build-up of catalyst or packing of the catalyst particles adjacent the ports I02.

The outer edge of each baiile is sealed to the interior of the wall of the reaction zone I0 and the inner edge of each baiiie has a vertical wall I I0 which forms a continuation of skirt I I2 which depends from the upper portion ofthe conical inlet I4. In this way the stripping zone is sealed off so that the only openings to the striping zone 44 are the ports I02. The stripping zone 44 is formed between the inner wall of the vessel I0 and the skirt ll2 so that an annular stripping zone or section is provided.

Strippin gas and volatile material stripped out of the mixture collect in the upper portion of the stripping section or zone. 44 under each curved baflle I08 and are withdrawn through openings II4 passing through the wall of vessel I0., The openings H4 communicate withpipes II6 leading to -a circular manifold II8 exterior to the reaction vessel I0. i The stream of stripping gas and I volatile material from manifold II8 is passed through vertical line I22 and in this way is by-' passed around the dense bed or mixture 24 in the reaction vessel I0 and is injected into the dilute phase 28 through valved line I22 or into the upper conical space of the reaction vasel through valved line I22" which opens through the top conical portion I22" 0! the reaction vessel. In some cases it may be preferredto introduce the gaseous fluid from line I22 into the upper ccnical space to avoid changing the velocity in the dilute phase 28 directly above the bed 24.

The stream of stripping gas and volatile material is introduced upstream of the separating means 88 so that entrained catalyst or contact particles are removed in passing out of the reaction vessel through the separating means 36. A valve I23 is provided for line I22 and is used as a control means as will be hereinafter described in greater detail. The line I22 is provided with a valved line I24 for removing stripping gas and volatile material from the system when it is not desired to return the stripping gas and volatile material to the reaction zone or vessel I0.

Providing the by-pass line I22 is an improvement over other forms of strippers because the stripping gas and the stripped out material does not have to pass up through the densebed or mixture in the reaction zone or vessel I0. Using the by-pass line I22 in the design of new plants, it becomes unnecessary to allow for the volume of stripping gases when designing the reaction vessel and a considerable decrease in the diameter of the reaction vessel is thus effected. Furthermore, in applying my invention to existing plants, a considerable increase in capacity is possible by providing the by-pass line I22 for by-passing the stripping gases around the dense bed.

The stripping zone or section 44 is provided I with rows of radial baffles arranged one above the other. Each baille is of inverted V shape in cross-section. The top row I28 of bafiles I29 is preferably formed of larger baflles than the remaining rows. The bafiies in the top row are arranged to have the apex I32 of certain of the baflles directly below ports I02. The dense phase catalyst from the reaction vessel I0 is divided by the sloping sides of the baflles I29 into two streams flowing down in opposite directions.

The next lower row of bailles I33 is arranged to have the apex I34 of every other baille directly be-.

low the opening I38 between the adjacent lower ends of the bafiles of the top row I28. The next two rows of baiiles I30 and I42 are also arranged in ofiset or staggered relation so that the apexes of the bafies are beneath openings between the bottoms of the sloping sides of the bafiles of the next higher row to further subdivide the downfiowing streams of solid particles.

Stripping gas, such as steam, flue gas, or inert gas, is introduced into the bottom portion of the stripping section or zone 44 through line 46 and concentric circular distribution pipes I44 and I46 provided with openings in the top portions thereof. The velocity of the gas rising between adjacent baffles, that is, at the points of minimum cross-section, may range from ft./second or less to about 1.5 ft./second. The valves I04 associated with the ports I02 may be manually operated to select the desired rate of flow of spent catalyst from the reaction zone or vessel I0 into the stripping section 44 or they may be automatically controlled. The amount of catalyst passing to the stripper is controlled so that the particles do not fill the stripping sections andv ascaaea 7 therefore the stripping is carried out in the dilute phase.

The opening lit for the removal of stripping gas from the upper portion oIthe stripping section is located between two of the ports I02 and as high up as possible in order to minimize the carry-over of catalyst from the stripping section into the reaction zone Ill.

The stripping medium may be steam or any other suitable inert gas. Air may also be used it proper precautions are taken to minimize the flow of this gas during upset conditions. Ii. air is used as a stripping medium, it will burn some of the carbon on the catalyst particles in the lower portion of the stripping section and in this way produce inert flue gas which is very suitable for removing hydrocarbon gases or volatile material in the upper portion of the stripping section from the catalyst or contact particles introduced at that point.

Where an inert gas is used for stripping it may be desirable to remove the stripping gas from the top of the stripping section to recovery means other than the separating'means 36 shown in the upper portion of the reaction vessel Ill. The reason for this is that in some of the existing plants the facilities are limited and the inert gas leaving the top or the stripping section, it passed to the regular outlet 42 of the reaction zone, would cause considerable overloading of the equipment. However,-in most instances this will not be the case because only a very small amount of stripping gas is needed for stripping catalyst in my improved stripping vessel.

As above pointed out, the level 26 of the dense material or bed 24 is automatically controlled in the reaction vessel I and the level of the stripped catalyst or contact particles collecting in the conical bottom 48 of thereaction vessel It is automatically controlled, it only becomes necessary to set the catalyst circulation rate. This may :be done conveniently by using the valve I23 in by-pass line I22 which conveys the stripping gas from the top of the stripping section to the top of the reactor I0. This valve may be a rather loose fitting butterfly valve.

The stripping gas rate is set at some constant desired value so that by throttling the valve I23 in. by-pass line I22 the pressure on the stripping section 44 is raised slightly and in this way the pressure diiferential between the reaction vessel Ill and the stripping section 44 is decreased somewhat which in turn decreases the flow of catalyst from the reaction vessel II) to the stripping section 44. Opening the by-pass valve I23 has the opposite effect, that is, the pressure differential between the reactor and the stripping section 44 is increased and this increases the rate of flow of catalyst from the reaction vessel It to the stripping section 44. The valve I23 may be manually or automatically controlled.

If desired, the butterfly valve I23 may be used to adjust the temperature of the dense mixture or bed in the reaction zone or vessel I0. In case the temperature in the reaction vessel I0 falls below a desired value, the valve I23 would be operated to open slightly to bring about an increase in catalyst flow from the hot regenerated standpipe 92 to the reaction vessel I0. On the other hand, if the reactor temperature becomes higher than the desired temperature, the butterfly valve would be closed slightly to decrease the amount of hot regenerated catalyst being delivered to the reaction vessel from the regenerated catalyst standpipe 92.

Dilute Phase 93,-;

Spent Cat. rate Tons/Min 10.9 11. 0- 9. 06 1102 14.0 Stripping steam rateJ/Hr 1040 1410 2572 378) 6115 Pounds of equivalent hydrogen lus carbon per ton of cat. leavng the stripper in gaseous phase. 2. 82 2.03 0. 0. 38 2. Ill Stripping steam/Ton Cat. flowing 1.59 2.02 4.74 5.63 5.72

From these data, obtained in an upflow type fluid cracking plant, it is apparent that the pounds of combustibles associated with a ton oi stripped catalyst are approximately equal (2.82 vs. 2.94) for the two types of strippers but that the dilute phase stripper used less steam per ton of catalyst circulation (1.59 vs. 5.72). Also, when the comparison is made at approximately equal steam rates per ton of catalyst (5.63 vs. 5.72), the dilute phase stripper produced a catalyst of m 1011 less combustible content in the gas phase associated with the solid particles (0.38 vs. 2.94). 1

While I have .shown one form of apparatus and have given certain operating conditions, it is to be understood that these are by way of illustration only and various changes and modiiications may be made without departing from the spirit of my invention.

What is claimed is:

1. An apparatus of the character described including'a cylindrical vessel having a top outlet said stripping section, means for introducing stripping gas below said bailles, said vessel having a conical bottom for collecting stripped solid material leaving said stripping section and a bottom outlet for solid materials, partition means arranged between the top of said skirt and the internal wall of said vessel, valved openings in said partition means for controlling the flow of solid particles from said reaction zone to said stripping section and means for withdrawing gaseous fluid from the upper portion of said stripping section and from beneath said partition means.

2. An apparatus of the character described including a cylindrical vessel having a top outlet for reaction products, a conical feed member therein having a horizontally arranged periorated plate arranged in the lower portion of said vessel, said vessel providing a reaction chamber above said plate adapted to hold a dense fluidized mixture of solid particles having a level with a dilute phase thereabove, means for maintaining the level substantially constant, a skirt depending from said feed member and forming with the internal wall of said vessel an annular stripping section, rows of baflies in said stripping section, means for introducing stripping gas below said aaoaeco baiiles, said vessel having a. conical bottom for collecting stripped solid material leaving said stripping section and a bottom outlet for solid material and partition means arranged between the top oi said skirt and the internal wall of said vessel, valved'openings in said partition means for controlling the flow of solid particles'from said reaction chamber to said stripping section, a line for withdrawing stripping gas from the upper part of said stripping section and introducing it into the dilute phase in said reaction chamber, a valve in said last mentioned line for controlling the rate of removal of stripping gas from said stripping section to vary the pressure in said stripping section whereby the rate of flow of solid particles from said reaction chamber to said stripping section may be varied.

3. An apparatus of the character described including a cylindrical vessel having a top outlet for reaction products, a conical feed member therein having a horizontally arranged periorated plate arranged in the lower portion of said vessel providing a reaction chamber above said plate, a skirt depending from said iced member and forming with the internal wall of said vessel an annular stripping section, rows of babies in said stripping section, means for introducing stripping gas below said bailles, said vessel having a conical bottom for collecting stripped solid material leaving said stripping section and a bottom outlet for solid material, partition means arranged between the top of said skirt and the internal wall of said vessel, a plurality of valved openings around said partition means for controlling the flow of solid particles from the reaction chamber to the stripping section, the sections between said valves being arched to prevent accumulation and build-up of solid particles thereon when solid material is passed from said reaction chamber to said stripping section and means for withdrawing gaseous fluid from the upper portion of said stripping section.

4. An apparatus of the character described includinga cylindrical vessel having a top outlet for reaction products, a conical feed member therein having a horizontally arranged periorated plate arranged in the lower portion of said vessel providing a reaction chamber above said plate, a, skirt depending from said feed member and forming with the internal wall of said vessel an annular stripping section, rows of bodies in said stripping section, means for introducing stripping gas below said bailles, said vessel having a conical bottom for collecting stripped solid material leaving. said stripping section and a bottom outlet iorsolid material, partition means arranged between the top of said skirt and the internal wall of said vessel, a plurality of valved openings around said partition meansl'or controlling the flow of solid particles from the reaction chamber to the stripping section, the sections between said valves being arched to prevent accumulation and build-up of solid particles thereon when solid ,rhaterial is passed from said reaction chamber to said stripping section and means for withdrawing gaseous fluid from the upper portion of said stripping section, said means for withdrawing gaseous fluid from the upper portion of said stripping section including a plurality of outlets, one outlet being associated with the underside of each arched portion for removing gaseous fluid from said stripping section. 1

5. An apparatus of the character described including a cylindrical vessel having a top outlet collecting stripped solid material leaving said stripping section and a bottom outlet for solid material and partition means arranged between the top of said skirt and the internal wall of said vessel, valved openings in said partition means for controlling theflow of solid particles from said reaction chamber to said stripping section, a line for withdrawing stripping gas from the upper part of said stripping section and introducing it into the dilute phase in said reaction chamber, a valve in said last mentioned line for controlling the rate of removal of stripping gas from said stripping section to vary the pressure in said stripping section whereby the rate of how of solid particles from said reaction chamber to said stripping section may be varied, and means for maintaining a level of stripped contact particles in the conical bottom of said vessel substantially constant.

6. An apparatus of the character described including a cylindrical vessel having a top outlet for reaction products, a conical feed member therein having a horizontally arranged perforated plate arranged in the lower portion of said vessel providing a reaction chamber above said plate, a skirt depending from said feed member and forming with the internal wall of said vessel an annular stripping section, rows of bellies in said stripping section. means for introducing stripping gas below said bailies, said vessel having a conical bottom for collecting stripped solid material leaving said stripping section and a bottom outlet for solid material, partition means arranged between the top of said skirt and the internal wall of said vessel, a plurality of valved openings around said partition means for controlling the fiow of solid particles from the reaction chamber' to the stripping section, the sections between said valves being arched to prevent accumulation and build-up of solid particles thereon when solid material is passed from said reaction chamber to said stripping section and means for withdrawing gaseous fluid from the upper portion of said stripping section, said means for withdrawing gaseous fluid from the upper portion of said stripping section including a plurality of outlets, one outlet bein associated with the underside of each arched portion for removing gaseous fluid from said stripping section, a line communicating with the upper portion of said vessel, said outlets being in communication with said line to conduct gaseous fluid from said stripping section to said vessel.

7. An apparatus 01' the character described including a cylindrical vessel having a top outlet for reaction products, a conical feed member therein having a horizontally arranged perforated plate arranged in the lower portion of said vessel providing a reaction chamber above said plate. a skirt depending from said i'eed member and forming with the internal wall of said vessel an annular stripping section. means for in.-

troduiping stripping gas into the lower portion of said stripping section, said vessel having a. conical bottom for collecting stripped solid material leaving said stripping section and a bottom outlet for solid material, partition means arranged between the top of said skirt andthe internal wall of said vessel,'valved openings in said partition means for controlling the flow of solid particles from said reaction zone to said stripping section and means for withdrawing stripping gas and stripped-outmaterial from the upper portion of said stripping section.

8. An apparatus of the character described including a cylindrical vessel having a top outlet for reaction products, a conical teed member therein. having a horizontally arranged perforated plate arranged in the lower portion of said vessel providing a reaction chamber above said plate, a skirt depending from said feed member and forming with the internal wall of said vessel an annular-stripping section, means for introducing stripping gas into the lower portion of said stripping section, said vessel having a conical bottom for collecting stripped solid material leaving said stripping section and a bottom outlet section.

HOMER z. mam.

- REFERENCES crrEn The following references are of record in the file oi this patent:

UNITED STATES PATENTS Number Name Date 2,326,705 Thiele et a1 Aug. 10, 1948 2,341,193 Scheineman Feb. 8, 1944 2,363,874 Krebs Nov. 28, 19 2,391,336 Ogorzaly Dec. 18, 1848 2,414,852 Burnside et a1. Jan. 28, 1947 2,422,793 McAIe'e June 24, 1967 

